1. Field of the Invention
The present invention relates generally to a differential gear housing supporting apparatus for a vehicle and more specifically to a differential gear housing supporting apparatus for a vehicle of rear-wheel independent suspension type.
2. Description of the Prior Art
In an automotive vehicle of rear-wheel independent suspension type, it is necessary to elastically supporting the differential gear housing from the vehicle body. In the prior-art differential gear housing supporting apparatus, a rubber elastic member of peculiar shape is disposed between an inner cylindrical bracket fixed to the vehicle body and an outer cylindrical bracket fixed to the differential gear housing. The elastic modulus (ratio of stress increment to strain increment) of the elastic member of this type is as follows when the vehicle body vibrates up and down: in the case where the displacement of the rubber elastic member is relatively small and therefore the elastic member is not in contact with the outer cylindrical bracket, since the elastic member deforms in shear mode, the elastic modulus is relatively small (elastic member is soft); however, in the case where the displacement of the rubber elastic member is relatively great and therefore the elastic member is brought into contact with the outer cylindrical bracket, since the elastic member deforms in compression mode, the elastic modulus is relatively great (elastic member is hard). Therefore, the elastic modulus changes abruptly at a point of discontinuity. This causes a problem in that when the vehicle is quickly accelerated or decelerated and thereby the differential gear housing vibrates violently in relation to the vehicle body up and down, the rubber elastic member is repeatedly brought into contact with outer cylindrical bracket, thus making loud knock sounds. Additionally, the elastic modulus of such prior-art apparatus is not preferable. This is because the elasticity should be soft when the differential gear housing vibrates up and down slightly to the vehicle body, but be strong enough to restrict the displacement of the differential gear housing securely below a predetermined upper limit when the differential gear housing vibrates up and down violently, without any points of discontinuity. In other words, it is preferable that the vertical displacement of the elastic member increases sharply at high gradient with increasing load when vibration is not great but gently at a low gradient with increasing load to a restricted displacement limit when vibration is great, smoothly and gradually without any discontinuity.
A more detail description of an example of prior-art differential gear housing supporting apparatus will be made with reference to attached drawings under Detailed Description of the Preferred Embodiments.